現象
UNEXPECTED TOP-LEVEL EXCEPTION もいろいろなケースがあるので、一概に言えないのですが、以下のように ParseException: bad class file magic or version
の場合、コンパイルに使った Java のバージョンが合っていない可能性が高いです。
...省略
:app:preDexDebug
AGPBI: {"kind":"SIMPLE","text":"UNEXPECTED TOP-LEVEL EXCEPTION:","position":{},"original":"UNEXPECTED TOP-LEVEL EXCEPTION:"}
AGPBI: {"kind":"SIMPLE","text":"com.android.dx.cf.iface.ParseException: bad class file magic (cafebabe) or version (0034.0000)","position":{},"original":"com.android.dx.cf.iface.ParseException: bad class file magic (cafebabe) or version (0034.0000)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.cf.direct.DirectClassFile.parse0(DirectClassFile.java:472)","position":{},"original":"\tat com.android.dx.cf.direct.DirectClassFile.parse0(DirectClassFile.java:472)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.cf.direct.DirectClassFile.parse(DirectClassFile.java:406)","position":{},"original":"\tat com.android.dx.cf.direct.DirectClassFile.parse(DirectClassFile.java:406)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.cf.direct.DirectClassFile.parseToInterfacesIfNecessary(DirectClassFile.java:388)","position":{},"original":"\tat com.android.dx.cf.direct.DirectClassFile.parseToInterfacesIfNecessary(DirectClassFile.java:388)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.cf.direct.DirectClassFile.getMagic(DirectClassFile.java:251)","position":{},"original":"\tat com.android.dx.cf.direct.DirectClassFile.getMagic(DirectClassFile.java:251)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.command.dexer.Main.processClass(Main.java:704)","position":{},"original":"\tat com.android.dx.command.dexer.Main.processClass(Main.java:704)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.command.dexer.Main.processFileBytes(Main.java:673)","position":{},"original":"\tat com.android.dx.command.dexer.Main.processFileBytes(Main.java:673)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.command.dexer.Main.access$300(Main.java:83)","position":{},"original":"\tat com.android.dx.command.dexer.Main.access$300(Main.java:83)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.command.dexer.Main$1.processFileBytes(Main.java:602)","position":{},"original":"\tat com.android.dx.command.dexer.Main$1.processFileBytes(Main.java:602)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.cf.direct.ClassPathOpener.processArchive(ClassPathOpener.java:284)","position":{},"original":"\tat com.android.dx.cf.direct.ClassPathOpener.processArchive(ClassPathOpener.java:284)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.cf.direct.ClassPathOpener.processOne(ClassPathOpener.java:166)","position":{},"original":"\tat com.android.dx.cf.direct.ClassPathOpener.processOne(ClassPathOpener.java:166)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.cf.direct.ClassPathOpener.process(ClassPathOpener.java:144)","position":{},"original":"\tat com.android.dx.cf.direct.ClassPathOpener.process(ClassPathOpener.java:144)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.command.dexer.Main.processOne(Main.java:632)","position":{},"original":"\tat com.android.dx.command.dexer.Main.processOne(Main.java:632)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.command.dexer.Main.processAllFiles(Main.java:510)","position":{},"original":"\tat com.android.dx.command.dexer.Main.processAllFiles(Main.java:510)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.command.dexer.Main.runMonoDex(Main.java:280)","position":{},"original":"\tat com.android.dx.command.dexer.Main.runMonoDex(Main.java:280)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.command.dexer.Main.run(Main.java:246)","position":{},"original":"\tat com.android.dx.command.dexer.Main.run(Main.java:246)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.command.dexer.Main.main(Main.java:215)","position":{},"original":"\tat com.android.dx.command.dexer.Main.main(Main.java:215)"}
AGPBI: {"kind":"SIMPLE","text":"\tat com.android.dx.command.Main.main(Main.java:106)","position":{},"original":"\tat com.android.dx.command.Main.main(Main.java:106)"}
AGPBI: {"kind":"SIMPLE","text":"...while parsing com/kokufu/lib/Test.class","position":{},"original":"...while parsing com/kokufu/lib/Test.class"}
AGPBI: {"kind":"SIMPLE","text":"1 error; aborting","position":{},"original":"1 error; aborting"}
私の環境で Java のバージョンを調べてみると、以下のように 1.8 でした。
$ java -version
java version "1.8.0_20"
Java(TM) SE Runtime Environment (build 1.8.0_20-b26)
Java HotSpot(TM) 64-Bit Server VM (build 25.20-b23, mixed mode)
解決方法
2015/4/12 現在、Android Studio は Java 1.7 系でコンパイルするようですので、以下のように Java Library のコンパイルバージョンを下げます。
lib/build.gradle
apply plugin: 'java'
sourceCompatibility = '1.7'
Android Application のコンパイルバージョンを変更する
おまけですが、Android Application の方のコンパイルバージョンも変更することが出来ます。
以下のように Source Compatibility を選択すればオーケー。
現時点では 1.8 が選択肢にないです。
File → Project Structure